1. Field of the Invention
The present invention relates to a two-piece optical lens system for taking image, and more particularly to a miniaturized two-piece optical lens system for taking image used in a mobile phone camera.
2. Description of the Prior Art
The present invention relates to an optical lens system for taking image, from the object side comprises: an aperture stop, a first lens element and a second lens element, which is particularly suitable for use in the miniaturized portable machines with a high optical performance.
With the price coming down, the high resolution (1-3 million pixels) mobile phone cameras are usually made up of three lens elements. And the researchers are also required to design the optical lens system consisting of two lens elements, but such an optical lens system has a main problem, that is, the characteristic of an incident angle of the optical lens system will get worse.
However, the slightly poor characteristic of the incident angle of the optical lens system can still be used in the micro-lens elements of the solid image sensor such as CCD or CMOS.
Conventional plastic material is still not good enough to meet the demands for high optical performance, but in recent years, the plastic lens material is being refined constantly, and with the use of new material, the required optical performance has been realized.
Therefore, Japan Pat. Nos. 2004-170460, 2005-121685, 2006-154517, and 2006-178026 disclose several two-piece optical lens systems for taking image, and the aperture stop is located at the object side, so that the exit pupil of the optical lens system will be far away from the image plane and a good incident angle is ensured.
The disadvantages of the above patents lie in:
The cost of the first lens element made of glass of Japan Pat. No. 1 is high, and the refractive power of the second lens element is too weak, so that the chromatic aberration will not be sufficiently corrected.
The first and second lens elements of Japan Pat. Nos. 2 and 4 are made of the same material, so that the chromatic aberration will not be sufficiently corrected, and the high optical performance can not be ensured.
The second lens element of Japan Pat. No. 3 is a negative lens element has a convex object-side surface, the concave image-side surface is difficult to manufacture, and the peripheral edge of the second lens element leans to the image side, so that the back focal length can not be ensured.
The present invention mitigates and/or obviates the afore-described disadvantages.